Typical lateral-guiding structures used to form single-mode waveguides for quantum cascade lasers are deep-etched ridge waveguides, shallow-etched ridge waveguides or deep buried heterostructure (BH) waveguides. For high power applications, BH waveguides are typically favored due to a better capacity to dissipate heat when in operation because of the high thermal conductivity of the InP burying layers.
FIG. 1 shows a prior art BH structure. Quantum cascade laser (QCL) structure 100 has top electrode 105 and bottom electrode 110 sandwiching n-InP layer 103 and n-InP layer 102. Quantum cascade (QC) active region 108 is located between n-InP layer 103 and n-InP layer 102. Iron-doped InP burying layers 104 and 106 are located to the sides of QC active region 108. Ideally, iron-doped InP burying layers are perfectly insulating to force the drive current to flow from top electrode 105 to bottom electrode 110 or vice versa through QC active region 108. However, the iron doped InP material exhibits a thermally activated conductivity so that iron-doped InP burying layers 104 and 106 become conductive at elevated temperatures above about 50° C. Therefore, under conditions where the current causes heating to greater than about 50° C., the drive current may be partially shunted through iron-doped InP burying layers 104 and 106 avoiding QC active region 108 and degrading laser performance.